1. Field of the Invention
The invention relates to a semiconductor device for driving an electric motor.
2. Description of Related Art
An electric power steering system for a vehicle includes an electric motor, for example, a brushless motor, and a drive circuit. The drive circuit drives the electric motor. The drive circuit includes a switching device (semiconductor device), for example, a MOSFET. The switching device is installed on a substrate in, for example, a bare chip state. Bonding wires are joined to, for example, a source electrode of the switching device that is installed on the substrate. The bonding wires are joined to coils of the electric motor. The bonding wires connect, for example, the source electrode of the switching device that is installed on the substrate to the coils of the electric motor.
The drive circuit including the switching device is subjected to an inspection before factory shipment. The inspection is performed, for example, with an inspection probe placed in contact with a surface of the source electrode. For example, Japanese Patent Application Publication No. 2002-329742 (JP 2002-329742 A) and Japanese Patent Application Publication No. 2005-527968 (JP 2005-527968 A) each describe a semiconductor device inspection method in which a probe is used.
A surface of an electrode of a semiconductor device described in each of JP 2002-329742 A and JP 2005-527968 A has a region to which a bonding wire is joined and a region that an inspection probe contacts. The region to which the bonding wire is joined is contiguous with the region that the inspection probe contacts. However, this structure is formulated without giving special consideration regarding an inspection of a switching device for driving an electric motor. When the switching device for driving the electric motor drives the electric motor, a high electric current passes through the switching device for driving the electric motor. Therefore, in an inspection of the switching device for driving the electric motor, a special probe may be used instead of a commonly-used probe. This special probe is different in shape from a commonly-used probe. For example, an end portion of the special probe has a needlepoint-holder shape. The end portion of the special probe having a needlepoint-holder shape has a plurality of sharp contact portions that contact the surface of the electrode of the switching device. Alternatively, an end portion of a special probe is significantly thick. Therefore, the end portion of the special probe contacts the surface of the electrode of the switching device, at a wider region than an end portion of a commonly-used probe. Accordingly, the end portion of the special probe needs to be brought into contact with the surface of the electrode of the switching device after being accurately positioned with respect to the surface of the electrode of the switching device so that the end portion of the special probe does not contact the region to which the bonding wire is joined.
However, as described above, with the configuration in each of JP 2002-329742 A and JP 2005-527968 A, in the surface of the electrode of the semiconductor device, the region to which the bonding wire is joined and the region that the inspection probe contacts are contiguous with each other. Therefore, it is difficult to distinguish between the region to which the bonding wire is joined the region that the inspection probe contacts. Accordingly, when a worker performs an inspection using the probe, there is a possibility that the worker will erroneously bring the end portion of the inspection probe into contact with the region to which the bonding wire is joined, thereby making a scratch on this region. The scratch made by the inspection probe on the region to which the bonding wire is joined may cause the bonding wire to be poorly joined the bonding wire joined region.
Further, when the worker performs an inspection of the switching device using the inspection probe, it takes a long time for the worker to distinguish between the region to which the bonding wire is joined and the region that the inspection probe contacts, which reduces the production efficiency. As a result, the production cost increases. Meanwhile, an inspection of the switching device may be performed using an automatic inspection device. In this case, the following inspection method may be employed. The automatic inspection device first captures an image of the surface of the electrode of the switching device using a camera. Next, the automatic inspection device distinguishes between the region to which the bonding wire is joined and the region that the inspection probe contacts using an image processing device. Next, the automatic inspection device moves the inspection probe using, for example, a robot arm to bring the inspection probe into contact with the inspection probe contact region.
Even when the inspection of the switching device is performed using the automatic inspection device, there may be caused a problem similar to that when a worker performs an inspection of the switching device using the inspection probe. The problem is that it is difficult to distinguish between the region to which the bonding wire is joined and the region that the inspection probe contacts. The automatic inspection device may misidentify the region to which the bonding wire is joined as the region that the inspection probe contacts, or misidentify the region that the inspection probe contacts as the region to which the bonding wire is joined. In this case as well, there is a possibility that the automatic inspection device will erroneously bring the end portion of the inspection probe into contact with the region to which the bonding wire is joined, thereby making a scratch on this region. When an inspection of the switching device is performed using the automatic inspection device, a high-quality image processing device including a high-resolution camera is required to reliably distinguish between these two regions, which increases the cost.